Vertical synchronizing generator



March 2, 1954 R. E. GRAHAM ErAL VERTICAL sYNcHRoNIzING GENERATOR 3 Shets-Sheet l F'iled Aug. l0. 1951c ATTORNEY R. E. GRAHAM ETAL VERTICAL SYNCHRONIZINC GENERATOR March 2, 1954 S Sheets-Sheet 2 Filed Aug. l0, 1951 March 2', 1954 R. E. GRAHAM ErAL 2,671,133

VERTICAL SYNCHRONIZING GENERATOR Filed Aug; l0, 1951 5 Sheets-Sheet 5 WTA E j lili E j Fl CIQ C II.

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R. E. GRA HAM /NVENTORS'Q w HAM/50N y f. why

ATTORNEY Patented Mar. 2, 1.954

FFICE -v $671,133' VERTICAL SYNCHRONIZING'. GENERATOR Robert. El Graham;l Ch Harrison@ Gillette, N

phone Laboratories,

atham,. and? Charles.: W.

, assignors to Belllele- Incorporated, New- York,.

N. Y., 'a corporation of New Yor Application Angus# 1o, 19511,

Serial No; 241,243

llhis-v invention; relates to' synchronizing: sys'.- tems. More particularly it concemsfsynchroniz ingf systems which: make: use.` of composite sie:-` nais. having: diierent. `frequency componentsyfor utilizes composite slgnals, comprising relatively. short ,horizontalror tively longerfserrated;vertical or.field'sy-nclironz-v ing;V pulses, toscontrolfthe:vertical and `horizontal sweepf generators. the;- receiver for providing synchronization; with: thezscannng processfat. the transmitter.-

objectof this:- invention is to `improve., the

ratin'g `outthe longer iield` 'For eiectingthis-separation, the integrating. cir cuit is characterized by leakage; sufficient for eliminatingA the effect of the short Vhorizontal synchronizing pulsesbutV insuflicient to prevent the accumulation. of charge.. during. the; longer fieldf synchronizingpulses. about half. the expected. cumulative amplitude, iszmade the operating point for triggering the iieldl sweep generator. The triggering time then coincides with the accumulation of thechargeiin the integrating circuit. to this chosen operating amplitude;

However, this simple arrangement has for some time .pastheen know-n to be not too well'adapted for conventional interlaced scanning systems sinceinterlacine: results in non-uniformity be@ tween the even-y andvodd-numberedelds by each television frame: in the region. of the vertical synchronizing pulses. This non-uniformity, in turn, leads` to different triggering times as measured fromthestart of the iield synchronizingpulse fortwov successive fields, and'hence, uneven and inaccurate interlacing'; T o minimize the .-.diierence in Wave .formz inf themegion; or, the

Some point, usually vertical synchronizing. pu'lse'forl evenv and; odd-y numberecl scanningields, it is new the practice to'. insert? equffiliziner pulses, lat. half nline intervals,

eral, satisfactory,V for highffidelity receiverszit 'is usuallyV necessary tov rescrtto still moresophisticatedf arrangements toiobtain vthe desireddegree off accuracy in timing. The; presentsinventionis concern-edi vviththisprcblem.;

To this end-,- theseparaticn ofi the velcl. svn-v chrcnizing information is achieved by an: arrangement-in which the composite signal applied to. a frequencysensitive circuit, orlternet belowthe frequency of, the line synchronizing pulses, but abovethe. frequency ofthe eldgsynchroniznggpulses,y and thensubtractingthe.1ter output-1 derived fromfthe original ,input .composite signal; v

The invention; willbe better; understood with reference te: the vfollowing: more detaileddescriptiontalren in connection with, the accompanying draw-ings iii-Which:

Fig. 1 shows in block schematic form thel cir;- cuitryl of a typical television receiver;

Fig. Zshows inblockfschematic form a specific embodiment of a synchronizing:separator in ace.- cordancewith thepresent inventiom.

Eig. 3 shows in schematic circuit form the synchronizing separatorshownin'Fig. 2; and

Figs. 4A. to; 4G, inclusive, show Wave forms that arefuseful in describing the emhodimentfshoivn in-Fig; 2.

Referring now more. particularlyto thedrawr ings, in Fig. 1; there is shown' schematically' a typical television receiver iii; The transmitted radiofrequency television. signal isl receivedv by' the antennav li and, thereafter, in the radiojfree quencv stages lf2 itis amplied and converted tonnintermediate frequency. In the intermedi#l ate-frequency stages i3, thisA intermediate fre quency signalis ampliediurther, and: the video signal is-gdetected therefrom. In the; video stages i4; this; signal is again amplified., Ati this point', thev videosignal includes both the. picture and synchronizing. information. Because; it.: is; usual formation. This synchronizing information is a` which comprises a series of horiat line frequency interspersed with a series of serrated vertical synchronizing pulses recurring at field composite signal zontal synchronizing pulses recurring frequency. The wave form of a portion of this' composite signal is shown in Fig. 4A. This cornposite signal is thereafter applied to a synchronizing separator i6 which separates out the horizontal and vertical synchronizing pulses. These in turn are applied to the horizontal and vertical sweep generator l1 and i8, respectively, for providing the defiecting sweep signals which are applied to the appropriate deflecting means i9 of the viewing tube 20. The present invention is primarily concerned with improving the control of the sweep generators, more particularly the vertical sweep generator, and to this end provides an improved synchronizing separator arrangement which permits more accurate timing of the vertical sweep generator. The rest of the receiver may be as found in the typical cornmercial receiver.

Fig. 2 shows, in block schematic, a preferred embodiment of the invention, which will be described in connection with the wave forms shown in Figs. 4A to 4G, inclusive. The composite signal whose wave form is shown in Fig. 4A is applied to a low pass filter 2| which is designed to have an upper cut-off frequency below the line recurrent frequency so that effectively the short line pulses are filtered out while the longer held pulses are smoothed of their serrations. Accordingly, there is derived a signal having the wave form shown in Fig. 4B. This filter output is subtracted from the composite input signal in a subtractor 22 and the resultant therefrom has the serrated wave form shown in Fig. 4C. It can be seen that at this point there has beeneffected a displacement in amplitude level between the line andiield synchronizing pulses. 1t should be appreciated that the arrangement 23 shown within the dashed lines is a special form of high pass filter, which has a low frequency cut-off less than the line recurrent frequency but above the field recurrent frequency, and accordingly, it is possible to devise other filter arrangements which provide amplitude displacement in this fashion. This special forin of filter, which is a feature of the present invention, however, has been found to offer advantages of simplicity of structure and reliability of operation. Thereafter the output of the subtractor is applied to a clipper 23 whose level is adjusted to pass only the negative pulses which correspond to serrations in the vertical synchronizing pulses of the original input signal. The output therefrom, whose wave form is shown in Fig. 4D, now includes only vertical synchronizing information. This information comprises a series of negative pulses each of which corresponds to a serration in the vertical synchronizing pulses of the original input composite signal. These pulses can in some instances be used directly to control a vertical sweep generator and, accordingly, by setting the switch the output of clipper 23.

S (designated 24) at position 2, there can be derived a series of pulses suitable for control of a vertical sweep generator. Usually, however, it will be preferable to transform this synchronizing information to a form better suited for control of the vertical sweep generator. In such a case, corresponding to setting l of the switch S, this series of pulses is applied to a differentiator 25, and there will then be derived a series of short negative and positive pulses, corresponding, respectively, to the trailing and leading edges of This action is illustrated in Fig. 4E. .Ofthis series, either the positive or negative pulses can be used directly to control various. suitable forms of vertical sweep generators. Additionally, for control of sweep generators of the kind which utilizes a relatively long pulse rather than a series of short pulses. the output of dierentiator 25 is applied to a second clipper 25, adjusted to pass only unidirectional pulses, for example, positive pulses'as illustrated in Fig. 4F. Then by applying these pulses to pulse stretching means 21, there is obtained the relatively long pulse shown in Fig. 4G.

Fig. 3 shows in circuit schematic form an illustrative embodiment of the synchronizing separator shown in Fig. 2 represented by the upper setting of the switch S. The composite input signal which has the wave form shown in Fig; 4A, except that the polarities are reversed, is applied from the synchronizing stripper I5 by way of the low pass filter comprising the series inductance lill and the shunt capacitance W2 to the control grid of the tube V2 which together with the tube Vl forms a differential amplifier or subtractive network. The input composite signal is simultaneously applied to the control grid of the tube VI. The differential amplifier which comprises the tube Vl and V2 is designed to provide an output which is the arithmetic difference of the signals applied to its two input control grids. To obtain this dierential action, the cathodes of tubes Vi and V2 are coupled together and connected through the resistance R (designated H33) to the negative terminal of potential source or battery ill and the value of resistance R is chosen so that where gm is the transconductance of each of the tubes Vl and V2. The resultant output is derived across resistance 05 in the plate circuit of tube V2, and has the wave forms shown in Fig. 4C except that the polarities are reversed. This output is then clipped or rectified by the action of amplifier tube V3, whose control grid to which this output is applied is biased negative by voltage source H3. As a result, only positive pulses will be amplied. Accordingly clipping occurs and the output of tube V3 is a signal which has the wave form shown in Fig. 4D. As has been mentioned above, this signal can be used directly for the control of the vertical sweep generator if so desired. It can be seen that the synchronizing pulses shown in Fig. 4D correspond quite precisely to the serrations in the vertical synchronizing pulses of the composite signal shown in Fig. 4A. Accordingly, there is furnished a reliable and accurate source of synchronizing information. However, for the case where the form of synchronizing information shown in Fig. 4G is preferred, the output of'tube V3 is applied by way of a differentiating network comprising the capacitance E66 and resistance -i 01 to the control grid of the amplier tube V4 which is operated to respond only to positive input pulses. This clipping action can be achieved by properly biasing the control grid with respect to the potential source or battery |98. Thereafter the series of negative pulses derived on the plate of tube Vd are applied to the control grid of the tube V5 which is operated as a pulse stretcher. Pulse stretching is accomplished by charging the stray capacitance Cs across the output terminals llEi through tube V5 and by making the discharge path of this stray capacitance the high resistance Hi. There is then derived an output which has the Wave form shown in Fig. 4G where the vertical synchronizing pulse output rises sharply and precisely at the end of the rst vertical pulse serration allowing ample time for the return of the vertical sweep trace which has been at the opposite end of the screen.

it is to be understood that the specic arrangement described is merely illustrative of the general principles of the invention. Various other forms of filters, subtractors, clippers, differentiators, and pulse stretcher-s may be suitable in the construction of a vertical synchronizing separator within the scope of the present invention. Additionally, it is possible to simplify the circuitry by making some of the circuit elements do double duty, a consideration which has been disregarded in this particular arrangement in order to achieve a more orderly exposition of the principles of the invention.

What is claimed is:

1. A synchronizing separator for deriving vertical synchronizing pulses for a television receiver comprising an input source of a composite synchronizing signal including a rst series of pulses recurrent at the line television frequency and a second series of longer serrated pulses recurrent at the television field frequency, low pass lter means having its upper cut-off frequency below the line frequency and above the eld frequency, subtracting means supplied with the composite signal and the ilter output for deriving a difference signal, and clipping means supplied with said diiierence signal for deriving a series of Vertical synchronizing pulses.

2. A synchronizing separator for deriving vertical synchronization pulses for a television receiver comprising an input source of a composite synchronizing signal including a rst series of pulses recurrent at the television linefrequency and a second series of longer serrated pulses recurrent at the television iield frequency, low pass filter means having its upper cut-off frequency below the line frequency and above the eld frequency supplied with said composite signal for effecting a displacement in amplitude level between the first and second series, subtracting means for obtaining the difference between the filter output and composite signal, clipping means supplied with said difference for deriving a third series of pulses characteristic of the second series of pulses, differentiating means for providing a series of negative and positive pulses coinciding with the edges of said third series of pulses, and means utilizing the pulses of a particular polarity of said last-mentioned series for providing a vertical synchronizing signal.

ROBERT E. GRAHAM. CHARLES W. HARRISON.

References Cited in the file of this patent 

